This invention relates to a tensioner to provide a fixed tension to stress a chain or a timing belt which drives a cam shaft of an engine of a vehicle and the like.
In general, a tensioner is used as a chain tensioner or a belt tensioner to an engine. The tensioner operates to press the belt or the chain in a certain direction directly or indirectly so as to maintain a fixed tension when the chain or the belt occurs a slackness due to the extension and the friction thereof.
FIG. 4 shows a conventional example of such tensioner. As illustrated in Figure, a male screw member 2 is screwed with a female screw member 3 to be inserted within a casing 1. The male screw member 2 is screwed with the female screw member 3 at the former half portion of the male screw member 3 and a coil spring 4 is outwardly inserted through the latter half portion 4a of this coil spring 4 is inserted into a long groove 1a formed within the casing 1, another end portion 4b being inserted into a slit of the male screw member 2 thereby providing a rotation force to the male screw member 2. On the other hand, the female screw portion 3 penetrates a bearing 5 mounted to an open end (left end) of the casing, said top end (left end) being covered with a cap 6.
A hole of the bearing 5 through which the female screw member 3 penetrates, is formed to be a non-circular type such as a small oval type wherein an opposite faces are cut in parallel and the outer form of the female screw member 3 is also formed the same type. In such a construction the female screw member 3 is restrained the rotation thereof by the bearing 5, the rotation force from the male screw member 2 being changed to a propelling force of the female screw member 3 thereby the female screw member 3 advances in an escaping direction (left direction) from the casing 1. Accordingly, the cap 6 at the top end of the female screw member 3 always urges the chain or the belt whereby a fixed tension is allowed to be maintained. In FIG., the numeral 7 is an elastic boot which covers the open end of the casing 1, and 8 is a seal bolt screwed with the base end (right side) of the casing 1. Such tensioner includes a lubricant oil therein. These boot 7 and seal bolt 8 are attached in order to prevent the invasion of dusts into the casing 1 from the inside and the outside of the engine and the leakage of the lubricant oil within the casing 1 to the outward.
The above lubricant oil is necessary to secure a smooth operation of the tensioner.
However, in such a construction an inner volume of the casing 1 is not fixed, but changes according to the advancing or retreating of the female member 30. Accordingly, it is desirable to be able to secure a sufficient supply of the lubricant oil even if the above inner volume is changed. Such request is particularly important to a tensioner having a triple construction wherein a dimension of the whole device is shortened by combining three members of the male screw member, female screw member and the coil spring so as to pile them in a diameter direction because the volume of a cave in the casing thereof becomes smaller.
The tensioner having the above triple construction is developed in view of that the traditional tensioner described above necessitates to have a former half portion wherein the male screw portion 2 is screwed with the female screw portion 3, and a latter half portion wherein the coil spring 4 is outwardly inserted therethrough and that the whole device becomes long in an axial direction since the dimension of this male screw member decides the dimension of the device.
Therefore, in a traditional tensioner (FIG. 4), a bored holed is provided from the top end surface to the axial direction at the former half portion of the male screw member 2 to use the bored hole as an oil sump in order to supply a short amount of the lubricant oil due to the increase of the inner volume of the casing 1.
However, there is a problem that the formation of the bored hole at the above portion occurs a heat strain whereby the preparation of a male screw member 2 having a high accuracy is impossible because the former half portion of the male screw member 2 is a screwed portion with the female screw portion, said portion being subjected to the heat treatment during the preparing step.
In such a conventional tensioner, to secure a sufficient lubricant oil has been a subject of a long period of time.